Looks like blossom end rot.

It is a case of a rotting, similar to tomato BER.
It is like weather, you can talk about it but you cannot do anything about it.
I , personally, have come to believe that it has to do with the varieties of maters and pepps than growing conditions.
You never see this to happen to a chili pepper, growing right next to that pimento/bell pepper.

I have habanero peppers right next to them and they are all coming in just fine. Craziness.

Doesn't mean the habs are still not susceptible. I grow a lot of varieties and one thing I have noticed --- the smaller and less fleshy the pepper, the less chance of BER.

Does Mel's mix have any added calcium in it or instructions to add lime or gypsum or bone meal...something to supply calciium to the plants?

Try to find some water soluble calcium(maybe at a hydroponics store) and the season may still be salvageable. Next time, make sure you get some bone meal or gypsum in the mix well before planting.

You may also want to google "smokemaster witch's brew" He makes soluble calcium acetate out of dolomite lime and vinegar.

Good luck.

Kevin

the problem is trying to fruit sweet peppers in florida in the middle of summer.